1. Field of the Invention
The present invention relates generally to methods for stripping photoresist from a semiconductor device structure and, in particular, to methods for continuously moving resist stripper across the surface of a semiconductor device structure. More particularly, the present invention relates to resist stripper application methods that include exposing the resist stripper to a gas, to move the resist stripper across the semiconductor device structure, to thin the resist stripper, or to otherwise increase the rate at which the resist stripper removes photoresist from the semiconductor device structure.
2. Background of Related Art
In fabricating semiconductor devices, several material layers, including electrically conductive and insulative layers, are formed and patterned to build various structures upon an active surface of a semiconductor substrate, such as a wafer or other large-scale substrate formed from semiconductive material (e.g., silicon, gallium arsenide, or indium phosphide), thereby forming a semiconductor device structure.
The material layers formed over a semiconductor substrate are typically patterned by forming masks thereover. Photomasks are often employed. The formation of photomasks involves the use of a photoresist material that takes on a specific pattern as the photoresist material is exposed to radiation, such as one or more visible wavelengths of light, through a reticle. In this manner, the reticle and the radiation transmitted therethrough together define the specific pattern of the photoresist. The photoresist is then developed, or cured, so as to maintain the pattern and to form a photomask, which is commonly referred to in the art as a xe2x80x9cphotoresistxe2x80x9d or simply as a xe2x80x9cresist.xe2x80x9d Once the photomask has been formed, one or more underlying material layers may be patterned through the photomask, such as by way of wet or dry etching processes.
After one or more layers underlying a photomask have been patterned through the photomask to form a semiconductor device structure, the photomask is typically removed. Various processes are known for removing photomasks. Typically, a thin layer of a resist stripper is applied to the semiconductor device structure, such as by spraying the resist stripper onto the semiconductor device structure. Alternatively, a semiconductor device structure bearing a photomask is immersed, or dipped, into a bath of wet chemical resist stripper.
One type of resist stripper that may be used to remove a photomask from a semiconductor device structure is a wet chemical resist stripper, such as an organic resist stripper (e.g., phenol-based and phenol-free organic strippers) or an oxidizing resist stripper (e.g., solutions of sulfuric acid (H2SO4) and an oxidant, such as hydrogen peroxide (H2O2) or ammonium persulfate). Wet chemical resist strippers typically remove, or dissolve, the photomask with selectivity over (i.e., at a faster rate than) the material of the structures and material layers that underlie and that may be exposed through the photomask or upon removal of the photomask material from the semiconductor device structure. Some such wet chemical resist strippers include one or more types of active chemicals that remove photomasks by reacting with the material or materials of the photomasks. Thus, the concentrations of active chemicals in these wet chemical resist strippers decrease over time, thereby reducing the effectiveness of these resist strippers. Moreover, as the concentrations of reaction products increase in locations where further stripping is desired, the rate at which further reactions between the resist stripper and the photoresist may occur and, thus, the rate at which the photoresist is removed from the semiconductor device structure, are reduced.
As another example, ozonated water may be used as a resist stripper to remove a photomask from a semiconductor substrate. Typically, the water is heated to enhance the ability of the ozone dissolved therein to remove a resist layer from a semiconductor substrate. The heated, ozonated water may be applied to the resist-covered substrate by spraying. As those of skill in the art are aware, ozone effervesces from water relatively quickly. Thus, ozonated water resist strippers lose their effectiveness over time. In addition, as with other types of resist strippers, the rates at which ozonated water resist strippers remove photoresists may be reduced as the concentrations of reaction products increase in the resist stripper.
Conventional processes for applying resist strippers to resist, such as spraying or immersion, do not facilitate continuous movement of the resist strippers across the semiconductor device structure following application and may, therefore, permit the resist strippers to sit, or stagnate, on the resist. Stagnation of resist strippers is somewhat undesirable, however, as the concentrations of reaction products may increase during stagnation and stagnation may, therefore, reduce the rate at which the resist strippers remove photomasks from semiconductor device structures. In addition, when a wet etchant is employed as the resist stripper, the active chemical reactant or reactants of the resist stripper may react with the photomask and, therefore, decrease in concentration. As a result, in a stagnant area, the rate at which such a wet etchant resist stripper removes the photomask and, thus, the ability of such a wet etchant resist stripper to remove the photomask, decreases over time.
In the ozonated water example of a resist stripper, when the resist stripper is at rest, ozone escapes from the water into the atmosphere over time. As the concentration of ozone in the ozonated water resist stripper decreases, the effectiveness of the resist stripper, as well as the rate at which a photomask is removed from a semiconductor substrate therewith, are reduced.
When conventional stripping methods are employed, ozonated water resist strippers typically remove hard-baked photoresist at a rate of about 4,000 xc3x85 per second to less than about 8,000 xc3x85 per second.
The art lacks teaching of methods for introducing one or more gases into or onto a resist stripper to maintain a desired rate for stripping resist from a semiconductor device structure, as well as stripping systems for effecting such methods.
The present invention includes a method and system for stripping resists from semiconductor substrates while maintaining a desired rate of resist stripping. The method of the present invention includes applying a quantity of resist stripper onto a semiconductor device structure and directing at least one carrier fluid, such as a gas other than ozone, toward the resist stripper or forming at least one gas other than ozone in the resist stripper.
The resist stripper is applied to the semiconductor device structure in a manner that the resist stripper contacts at least a portion of a photomask, or resist, to be removed. For example, the resist stripper may be hot ozonated water that includes a concentration sufficient to remove the resist at a desired rate. Other types of resist strippers, such as wet chemical resist strippers, may also be used in accordance with teachings of the present invention. The resist stripper may be applied to at least a portion of the semiconductor device structure by spraying, in a stream, by dipping the semiconductor device structure in the resist stripper, or otherwise, as known in the art.
The resist stripper may be exposed to one or more gases or other carrier fluids prior to, during, or after application thereof onto a photoresist on the semiconductor device structure. The one or more other, non-ozone gases may thin the layer of resist stripper over the semiconductor device structure or move the resist stripper across a surface of the semiconductor device structure, both of which prevent the formation of or eliminate macroscopic drops of resist stripper on the semiconductor device structure. Alternatively, the one or more gases may be the product of one or more chemical reactions effected by or in the resist stripper, in which case the one or more gases are formed in the resist stripper. In any event, by exposing the resist stripper to one or more gases or other carrier fluids, the rate at which the resist stripper removes photoresist from the semiconductor device structure is increased.
As an example of the manner in which resist stripper may be moved across the surface of the semiconductor device structure, one or more gases under pressure, such as in a jet or stream of liquid or gas, may be directed at least partially across the surface of the semiconductor device structure so as to force resist stripper across the semiconductor device structure. This movement of resist stripper across the surface of the substrate prevents stagnation of the resist stripper and, consequently, prevents a reduction in the rate at which the resist stripper removes the photomask from the semiconductor substrate.
The one or more gases may be directed across the surface of the semiconductor device structure substantially simultaneously with the resist stripper, either by combining the gas or gases with the resist stripper or separately from the resist stripper. Alternatively, the gas or gases may be directed across the semiconductor device structure after the resist stripper has been applied to the semiconductor device structure. When the one or more gases are directed across the surface of the semiconductor device structure, the one or more gases force the resist stripper to move across the device structure.
The one or more gases may be directed across the surface of the semiconductor device structure from a central region thereof toward an outer periphery thereof. Alternatively, the one or more gases may be directed onto a surface of a semiconductor device structure near a peripheral edge thereof so as to move resist stripper across the semiconductor device structure. Application of one or more gases may also be effected in any alternative manner that facilitates the substantially continuous movement of resist stripper across the surface of the semiconductor device structure.
The one or more gases will preferably not react with (e.g., oxidize or otherwise react with or change the nature of) materials of structures or layers of the semiconductor device structure that are exposed through the photoresist or as the photoresist is removed from the semiconductor device structure. Gases that may be used in the method of the present invention include, without limitation, inert gases or gas mixtures, such as nitrogen or noble gases (e.g., argon), air, and gaseous hydrochloric acid.
The present invention also includes systems for applying resist stripper to semiconductor device structures in a manner that effects the inventive method. An example of such a system includes a source of resist stripper, a stripper application component for introducing resist stripper onto a surface of a semiconductor device structure, a gas source, and a gas application component for directing gas at least partially across the surface of the semiconductor device structure so as to move resist stripper across the surface. The stripper application and gas application components may be separate from one another or comprise the same component.
Other features and advantages of the present invention will become apparent to those of skill in the art through consideration of the ensuing description, the accompanying drawings, and the appended claims.